Conventionally, there is known a road-vehicle communication system that includes a roadside apparatus installed on a road and vehicle-mounted device mounted on a vehicle and performs two-way wireless communication between the roadside apparatus and the vehicle-mounted device. In this road-vehicle communication system, for example, a short-range communication system called DSRC (Dedicated Short Range Communication) is adopted.
The vehicle-mounted is capable of performing the short-range wireless communication with the roadside apparatus and receiving information provision from a center apparatus via the roadside apparatus. Specifically, only in a period when the vehicle is within a communication range of the roadside apparatus, two-way communication between the vehicle-mounted device and the roadside apparatus is possible. Information is provided from the center apparatus to the vehicle-mounted device via the roadside apparatus in this period.
The road-vehicle communication system can provide the vehicle-mounted device with information for supporting traveling such as information indicating that there is an obstacle such as a stalled vehicle ahead on a road or there is a junction ahead. Therefore, the road-vehicle communication system is extremely effective for preventing traffic accidents.
Incidentally, in recent years, an accident of collision of a forward traveling vehicle and a reverse-way traveling vehicle in a one-way road such as a toll road (a reverse-way traveling accident) frequently occurs and poses a problem. This reverse-way traveling accident is caused by, for example, a vehicle entering the toll road from an exit ramp by mistake or traveling an entry road in a reverse way in returning from a service area or a parking area (hereafter referred to as SA/PA) to a main lane.
As a measure for preventing reverse-way traveling in the toll road, for example, attention is called by a road sign or a road surface display that indicates that a road is a one-way road. A technique for warning, using a road-vehicle communication system, a driver that the driver is traveling in a reverse way is proposed (e.g., Patent Document 1).
The road-vehicle communication system described in Patent Document 1 transmits entry information from a roadside apparatus to vehicle-mounted device, for example, in an interchange of a toll road and outputs sound such as “enter a toll road” or “please be careful about a reverse-way traveling” to warn the driver and call attention of the driver to not travel in a reverse way.    Patent Document 1: Japanese Patent Application Laid-Open No. 2007-102443